[Topics] Remove the random shuffle step

At the end of BrowsingTopicsServiceImpl::GetBrowsingTopicsForJsApi(),
the topics are sorted by id, version, etc., which should no longer
reveal the epochs' ordering. There's no need to random shuffle.

Bug: 1378430
Change-Id: Id9e09d6fef995b6553a28fd03729f3b0d443cfe7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3980495
Commit-Queue: Yao Xiao <yaoxia@chromium.org>
Reviewed-by: Josh Karlin <jkarlin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1063815}